Astron. Astrophys. 353, 25-40 (2000)
We summarize the main conclusions of our analysis of the
AGNs from the ROSAT surveys
in a wide range of depths:
Like previous works, we find a strong evolution of the SXLF up to
and a levelling-off beyond this
We have tried to find a simple analytical description of the
overall SXLF. Our combined sample rejects the classical PLE model with
high significance. The PDE model has been marginally rejected
statistically and also overproduces the soft CXRB.
We have found that an LDDE form (LDDE1), where the evolution rate
is lower at low luminosities, gives an excellent fit to the overall
SXLF. The extrapolation of the LDDE1 form produces
of the estimated extragalactic soft
Another form of LDDE (LDDE2), which equally well describes the
overall SXLF from our sample, produces
of the extragalactic soft CXRB. These
two LDDE models may be considered as two possible extreme cases when
one considers the origin of the soft CXRB.
The evolution of the number density of luminous QSOs in our sample
has been compared with that of optically- and radio-selected QSOs. Our
data are consistent with constant number density at
, while optically- and
radio-selected QSOs show a rapid decline. The statistical significance
of this difference is just above 2.
Including more deep ROSAT surveys would trace the behavior with
a better significance.
© European Southern Observatory (ESO) 2000
Online publication: December 8, 1999